The present invention relates generally to integrated circuits and in particular to a method and circuitry for isolating internal circuitry of an integrated circuit from its I/O terminals.
Integrated circuits developed for applications such as data or telecommunication systems are often required to comply with certain transmission protocols and standardized interface specifications. Some transmission protocols require that the input/output (I/O) circuitry inside an integrated circuit that connects to the transmission line not draw excessive currents from the transmission line. Thus, the integrated circuit must be designed such that the internal I/O circuitry can be electrically isolated from the transmission line. Under normal operating conditions, transistor switches can be used such that when turned off the internal I/O circuit is disconnected from the I/O terminals (or pads). However, the problem arises when power is removed from the integrated circuit and conventional circuits fail to operate properly to control the isolation transistor switches. The transmission protocols still require minimum current loading by the integrated circuit even under no power condition.
There is therefore a need for circuitry that is capable of isolating internal I/O nodes of an integrated circuit from the I/O pads.